The present invention relates to a unique, carboxylated cellulosic material and to a process for preparing the same. This novel cellulosic material, which will be referred to herein as "carboxylated cellulose ester" or "XAE", demonstrates a surprising and unexpected combination of properties which makes it useful, for example, in various coating applications, such as automotive finishes, wood coatings, pigment dispersions, inks, lacquers, etc., which will be described in further detail hereinafter.
The oxidative treatment of cellulosic materials has been studied for many years. It is known, for example, that cellulosic materials, including cellulose (in the form of pulp, lint, etc.), cellulose esters, or cellulose ethers, can be bleached by treatment with oxygen or ozone. However, it is widely recognized that such a bleaching treatment occurs extremely rapidly and does not involve any significant reaction with the cellulosic substrate, as evidenced by absence of by-products, little, if any, reduction in molecular weight, etc.
It is further known that cellulose derivatives, such as cellulose esters and cellulose ethers, can be degraded oxidatively by treatment with air or oxygen at elevated temperatures. See, for example, Proceedings of the Academy Of Sciences of the U.S.S.R., Vol. 114, p. 569-571 (1957). It is disclosed therein that oxidative degradation of such cellulose derivatives is accompanied by a reduction in the degree of polymerization and the appearance of by-products, such as acids and aldehydes, caused by cleavage of ether and ester groups. There is no indication that any further chemical processes, such as carboxylation of the cellulosic residue, occurs during the oxidative degradation of cellulose esters.
Chemical modification of cellulose ethers is further described in a number of publications, such as "Mechanism of Ozone Attack on .alpha.-Methyl Glucoside and Cellulosic Materials", Journal of Polymer Science: Part A-1 Vol. 4, pages 2683-2703 (1966), by A. A. Katai and Conrad Schuerch; U.S. Pat. Nos. 4,226,849; 4,316,982; and 4,357,469. None of these references relates to cellulose esters or processes for the chemical modification thereof.